1. Field of the Invention
The present invention relates to a machine tool controller.
2. Description of the Related Art
In a machine tool, a motor is used as a drive source (spindle motor) for driving a spindle provided with a workpiece and a tool and as a drive source (feed axis motor) for driving a feed axis which moves the spindle and a workpiece. In such a machine tool, alternating current power supplied from an alternating current power supply side is once converted by a rectifier to direct current power and then the direct current power is further converted by an inverter to alternating current power, and such alternating current power is used as drive power for the motor provided for each drive axis. A machine tool controller controls an alternating current output from each inverter to have a desired voltage and a desired frequency, thereby controlling a speed, a torque, or a position of a rotor of each motor connected to an alternating current side of each inverter.
When such a power failure that a motor drive device which is used for the machine tool and a peripheral equipment thereof fails to continue to operate occurs, it is possible that a problem in an operation of the motor may occur, and some problems, such as damage and deformation of the motor drive device which drives the motor, the tool connected to the motor which is driven by the motor drive device, a workpiece which is machined by the tool, a manufacturing line including the motor drive device, and the like, may occur.
Thus, for example, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2011-209936, it is common that the machine tool controller includes an element which detects a power failure of an input power supply used to drive the machine tool, and outputs an alarm and performs a protection operation for avoiding or minimizing the above problems when a power failure is detected.
Further, in a field of machine tools, an alarm generation history is stored in the machine tool controller to be widely used in grasping an operation state of the machine tool and the like and trouble shooting. In addition, not limited to the above, also in a general machine, when a power supply abnormality occurs, information relating thereto is stored, and later the information as stored is utilized for some operations.
For example, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2015-43794, in a washing machine, an occurrence date and time of a power failure of the input power supply and an operation state are stored in a storage unit, and after recovery from the power failure, a content of the storage unit is read and if possible, an operation at a time of the power failure is resumed.
In recent years, as motor control techniques make progress, machining precision of the machine tool has remarkably improved, whereas in machining which necessitates high precision, such as finish machining, even due to a slight power supply abnormality, such as a temporary voltage drop, a slight voltage drop, or an instantaneous power failure, an influence on machining precision is feared. Thus, to realize high precision machining in the machine tool, such some measures as to enable a grasp of a situation relating to not only a power failure but also a slight power supply abnormality have been demanded.
Such a slight power supply abnormality fails to satisfy power failure determination conditions and thus fails to be detected as a power failure, and machining of a product by the machine tool continues. As a result, an alarm is not generated, and as a matter of course, an alarm generation history is not stored. Thus, there has been a problem that when a defect in a product as machined by the machine tool occurs, specifying a cause in trouble shooting, i.e., whether the cause thereof lies in a slight power supply abnormality or in another factor is difficult.
On the other hand, if power failure determination conditions are relaxed such that determination as a power failure is easily made, even a slight power supply abnormality is determined as a power failure, a protection operation is performed so that the machine tool is stopped, which consequently leads to reduction in a percentage of machine usage. Since once a protection operation is performed, the manufacturing line is stopped to generate economic losses, in machining which does not necessitate high precision, minimizing execution of a protection operation is preferable.